Hard disc light starts for no reason

Hi There
From time to time my hard disc light will come on for no reason (no programs running ) and computer locks. Can also happen if am using Firefox or Word or similar, even when I have good free memory (say 200mb out of 500mb) (sony Laptop running XP) When this happens the desktop icons will not respond and cannot open any program. Cannot use the start button to restart . Can be like this for ten minutes or more.
Use ccleaner on a daily basis to remove unwanted files and also its registry cleaner. Update and run Norton daily and never find any problems. The only other word that I can add is HELP !

Whilst this problem may not be new to the group I am and so would not have seen the origonal answers

Hi There
From time to time my hard disc light will come on for no reason (no programs running ) and computer locks. Can also happen if am using Firefox or Word or similar, even when I have good free memory (say 200mb out of 500mb) (sony Laptop running XP) When this happens the desktop icons will not respond and cannot open any program. Cannot use the start button to restart . Can be like this for ten minutes or more.
Use ccleaner on a daily basis to remove unwanted files and also its registry cleaner. Update and run Norton daily and never find any problems. The only other word that I can add is HELP !

Whilst this problem may not be new to the group I am and so would not have seen the origonal answers

No I would not say hot -- it is warm on the top surface on the righty hand side above the HD and warmer around the rear air duct -- do you think that air duct is dust blocked and if so should the air be blown into the duct itself when the macine is cold.
Wait to hear from you

Sorry Jezza 70 only just seen your post as it is a one-liner below my lengthy first post
Have recently done a hardware test with Fix-it and it reported all OK --- is there a better utility that you would suggest